1. Field of the Invention
The present invention relates to a system and method for performing an optical read and a RF read on a carrier unit. More particularly, the present invention relates to a system and method for performing an optical read prior to establishing communication between a RF interrogation device and a RF tag, and more particularly to a system and method for performing a bar code read prior to establishing communication between a RF interrogation device and a RF tag.
2. Description of the Related Art
Given the fast pace of commerce today, it is imperative that the movement of articles of manufacture (“goods”) from one location to another be tracked. Goods must be identified quickly, including information concerning the source of the goods, the location of the goods and the destination of the goods. When goods are stacked on pallets in a warehouse, on a loading dock, in a railcar, or in any similar temporary storage environment, it is imperative that the identification of the goods be made quickly and relatively inexpensively so inventory of the goods can be had as the goods are transported further down the commerce stream without undue delay.
The use of passive RF transponder devices is common. These devices require no internal power source and can be manufactured relatively inexpensively in mass quantities. In a passive tag system, a radio transponder uses radio frequency energy in a RF interrogation device (tag reader) to communicate with a passive RF tag. An energizing signal is transmitted by the RF interrogating device, which creates an energizing field. This field powers up the passive transponder RF tags within the field and enables the RF tags to transmit their identity, and other data, to the interrogating device.
Regarding RF tags, there are several common varieties. RF tags for articles, or goods, are typically passive, deriving all their operational power from a RF interrogation signal. Active tags having a battery or other internal power source are typically used for vehicle, or other large object, tracking and/or identifying. A passive/active RF tag includes a passive receiver section and an active processing, storage and/or transmitting section. One-bit tags are generally used in an electronic article surveillance (EAS) system in retail stores as a security measure to protect against theft. For one-bit tags, the logical state of the security bit is detected by an interrogation device near the store exit. An alarm will sound if the article containing the RF tag passes through an interrogation signal from the interrogation device with an incorrectly coded tag, i.e. a tag for an unpaid article coded as not yet being permitted to leave the store premises.
For passive RF tag operation, frequently a principle called backscatter modulation is used for data communication from the RF tag to the RF interrogating device. The energizing field created by the interrogating device is typically in the form of a carrier wave signal at a fixed frequency. The energy of the transmitted carrier wave signal is received by the coil, or antenna, of the RF tag, is rectified, and is used to power the RF tag. The carrier may be in the form of a header that is transmitted for a sufficient period of time, e.g. 30 milliseconds, to enable the RF tag to “charge up” prior to communicating with the interrogating device. After the charge up period, the RF tag device is able to transmit control signals, timing signals, data or otherwise communicate with the interrogating device.
The RF tag generates a signal for the interrogating device in the form of a data stream, which may include a clock signal and data stored in the RF tag. This generated signal may be in the form of a modified manchester encoded signal at a second frequency (e.g. 10 KHz) that is shifted from the original interrogating signal (e.g. 915 MHz) by the clock rate of the RF tag. The data stored in the RF tag is used within the RF tag to drive a shorting, or shunt, transistor connected across the RF tag antenna. This has the effect of changing the reflectivity of the RF tag antenna with respect to the interrogating signal from the interrogating device and causes some of the received energy from the interrogating device to be reflected back towards a receiver on the interrogating device. The RF tag acts as a field disturbance device by reflecting the incident RF interrogation signal in a coded manner. The energy reflected by the RF tag may take the form of data packets. A simple receiver on the interrogating device, using the RF tag signal as a local oscillator, can decode the received signal from the RF tag and extract the encoded data.
Optical scanning devices are used to read a bar code printed on a label which is attached to individual goods or attached to a shipping container, a storage container, a box, a shipping pallet, or to any similar container, herein referred to as a “carrier unit”, for transporting or temporarily storing goods. Optical scanners typically perform a read of one-dimensional coded images (e.g. bar codes) or a read of two-dimensional coded images. The two-dimensional codes typically include more information than the one-dimensional variety, but two-dimensional readers typically cost more than one-dimensional readers.
Performing an optical read on a bar code has associated problems. The operator of the reader must be in line of sight with the bar code and must be close enough for optimum performance of the reader. A dirty scanning window on the reader, or a dirty or torn bar code label will cause a misread leading to errors. Additionally, information encoded in the bar code cannot be changed without printing another bar code that contains the new information.
Using a RF tag reader also has associated problems. In a large storage facility, such as a warehouse, using a RF tag reader alone to identify and track goods may be difficult and/or inefficient. A RF tag reader sends out an interrogation signal which is responded to by one or more tags which have received the interrogation signal using a chosen preestablished protocol. Unfortunately, the physical location of the carrier unit used to store the goods may be indiscernible.
Neither an optical reader nor a RF reader can, by itself, quickly and accurately ascertain both the physical location of the desired carrier unit or individual goods and identify, and read from and/or write to a RF tag associated with the desired carrier unit or individual goods.